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Unfortunately, i can't say that I have any experience with db meters. If you get one, be sure to bear in mind the distance from the sound when you test. You should establish a set range to test sound from, so that you can accurately compare the performance to other things. You might know this already, you seem like you are well versed in your physics knowledge. Of course, there is probably some standard distance that i'm unaware of. Good luck with finding one!

My experience with fairly cheap dB meters (same sort of price range) is that they'll average too much to really be useful. The Fast and Slow settings mean they'll either average over about 1/10th of a second or a whole second. This, of course, is far too long to get a good peak reading of a firing crack.

I have found a way to use it meaningfully, using it to get a reference dB level for a steady sound, then using a separate sound recording to compare the reference sound and the peak level (in Audacity, or something similar), then working out what the peak dB should be from that.

But it's no good for recording the dB level of a report directly.

It might give you a vague comparative measure, but mine usually reads well under 100 dB when I've tried it for measuring reports, and that's clearly false. Done in such a way I get a proper reading, I've recorded SPLs of nearly 160 dB @ 1m. (And you wonder why I use hearing protection.)

That's a discrepancy of in excess of six orders of magnitude. In short, don't expect it to read "gunshots" properly.

If you don't need absolute measurements, relative levels can be recorded on a laptop with proper manual gain control. A is louder than B and the Amplituede is douple so you know A is 6 DB louder. Distortion and clipping are easy to spot. Attenuation pads can be added for measuring loud sounds.

I was going to suggest audacity an a cheap mic... it seems it would be good enough for this purpose

Most pressure transducers are for higher pressure and lower frequency. A mic with a flat frequency response will pick up a lot of sound the pressure transducer misses. A pressure transducer is good for picking up the primary pressure wave from a large volume event such as Vera or 40MM cannon fire, but will miss the bulk of higher order sound.

Audacity and a Mic is fine if you have a way to set calibrated levels so a recording made on Tuesday is exactly the same gain as a recording made on Friday. Most PC volume controls with a slider do not allow setting an absolute value for gain. A same day test where the volume is never touched would work fine. Audacity has some nice tools for adding filters and other advanced features.

Most all condenser microphones sold for PC's have a FET amplifier in them which is powered by the sound card. They tend to be unsuitable for loud sounds and will clip the signal before it gets to your instrumentation (PC sound card). Using an external sound board or mixer and then feeding into the line level inputs is recommended. A quality dynamic mic or pro condenser mic suitable for high SPL levels is recommended.

Be aware, many computer mic inputs are filtered for speech and are far from flat. They design them to help phone applications filter out background noise below and above talking frequencies.

Here is an example of a poor mic clipping the signal long before the sound card reaches peaks.

Here is a waveform where the sound card was fed too much signal and the signal reached the hard limits of the sound card. Simply adding an attenuator to this mic would fix the waveform so it would be within limits.

Yeah, I think Bikini gauges are possibly a little too high in the SPL range.

You'd need to be able to make discs that could burst at around 1 - 1000 pa (corresponding to 94-154 dB, the kind of range you'd need to cover).The 1 Pa disc would tear if a mouse coughed on it, a 10 Pa disk would tear in a mild breeze, and even the 100 Pa disc would be pretty frail.

Good luck making something that flimsy and actually getting far enough to use it.